The optical filtering effect achieved in the present invention is based on the well known fact that light intensity spatial distribution in the interference region between two optical waves can change significantly depending upon the degree of mutual coherence of the interfering waves. This spatial distribution appears in the case of either wavefront division (related, for example, to Young's two-beam interference) or amplitude division (related to parallel plate interference, Fabry-Perot filter interference, dielectric multilayer interference and, finally, to Bragg hologram interference).
Simply speaking, the goal is to obtain an interference pattern for coherent illumination, e.g., laser light, and no interference for incoherent illumination, e.g., ambient light. The degree of coherence can then be used as the key parameter for determining the interference pattern in general and the division of reflected and transmitted beams in particular. The net result is a spectral response (i.e., reflectivity and transmitivity) from a plane parallel plate, Fabry-Perot filter, dielectric multilayer, or Bragg holographic structure which differs for coherent (laser) light relative to poorly-coherent (ambient) incident light. This phenomenon can be significantly amplified, assuming certain coherence/geometrical conditions are satisfied, leading to the optical coherence dependent filtering effect of the present invention.